2. List the properties that decide the state of matter.
3. What is meant by melting point and boiling point of a substance?
4. What are the effects of heating on matter?
5. Give reasons:
(a) Solids are rigid and retain their shape.
(b) Liquids and gases expand on heating.
(c) A solid does not flow but a fluid flows.
Answers
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Answer:
The kinetic energy of particles due to their motion. Force of attraction between its atoms. Interparticle space.
3. The melting point is defined as the temperature at which solid and liquid phases are in equilibrium, whereas the boiling point is the temperature at which the vapour pressure of a liquid is equal to the external pressure.
4. Following are the effects of heating
1) Expansion:
When heat is added to any substance, the particles gain energy and vibrates(with more speed) or vigorously about their fixed positions, forcing each other further apart.
Order of expansion Gas>Liquid>Solid
2) Increase in temperature:
When heated there is increase in kinetic energy and particles move at higher speed. Since temperature is a measure of average Kinetic Energy, the temperature increases.
3) Change in state:
When there is phase change of solid to liquid and liquid to gas, temperature remains constant but there is absorbing of heat, heat absorbed is used to separate particles and there is no rise in temperature.
5. a) Molecular motion for the particles in a solid is confined to very small vibrations of the atoms around their fixed positions; therefore, solids have a fixed shape that is difficult to change. Solids also have a definite volume; that is, they keep their size no matter how you try to change them.
b) Liquids expand for the same reason, but because the bonds between separate molecules are usually less tight they expand more than solids. This is the principle behind liquid-in-glass thermometers. An increase in temperature results in the expansion of the liquid which means it rises up the glass.
Molecules within gases are further apart and weakly attracted to each other. Heat causes the molecules to move faster, (heat energy is converted to kinetic energy) which means that the volume of a gas increases more than the volume of a solid or liquid.
However, gases that are contained in a fixed volume cannot expand - and so increases in temperature result in increases in pressure
c)In solids there is a strong force of attraction between the molecules and the space between them is very negligible. The molecules are therefore, not free to move. They merely vibrate about their mean positions. But in the case of liquids, the molecules are not very closely packed. They do not attract each other as strongly as the molecules of solids. Thus, the intermolecular spaces are larger and the molecules are able to move about more freely. This makes a liquid flow.
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